Gondola railcars are used to carry bulk material such as coal and the like, and may be rotated by rotary dump equipment about their longitudinal axes to an inverted position for unloading, without uncoupling from adjacent railcars. Typically, these cars include one rotary coupler which remains coupled to a following car, and one nonrotary coupler which is coupled to a rotary coupler of a preceding car.
To provide added load carrying capacity, many of these cars have a depressed center section in which the floor of the car extends below the side sills in a curved configuration, either parallel or perpendicular to the center line of the car. Examples of cars with the parallel curved depressed center section, which commonly are referred to as "bathtub" gondolas, are illustrated and described in U.S. Pat. Nos. 3,713,400 and 3,817,189. An example of a car with two perpendicular curved depressed center sections, which commonly is referred to as a "twin tub" gondola, is illustrated and described in U.S. Pat. No. 4,212,252.
In depressed center section gondola railcars such as those just mentioned, buff and draft forces are transmitted between the couplers via the side sills. Shear plates transmit buff and draft forces between center stub sills located at the ends of the car and the side sills. In many practical cases, the shear plates are fabricated from steel sheets as thick as 3/8 inch to 1/2 inch and, in some cases, it is necessary to provide additional reinforcement to the shear plates in the form of diagonal or longitudinal bracing. Despite such reinforcement, however, the shear plates and side sill connections tend to be susceptible to fatigue cracking and other types of failure. Additionally, the shear plates, together with any such reinforcement, tend to increase the weight of the car. Accordingly, the side sill load path employed in such gondola railcars tends to be unsatisfactory.
Rising fuel and other costs, together with increased maintenance-of-way costs, have created the need for a gondola railcar which is economical to operate and offers a rapid return on investment. Conventional steel gondola railcars of the type mentioned above tend to be unsatisfactory from this standpoint, mainly because they feature designs which tend to sacrifice operating economy, in particular weight savings, in favor of structural integrity. The reaction to failures discussed above stems from and exemplifies this philosophy. Another reason for this is that the steel sheets, which make up the side and end walls and bottom of steel gondola railcars, are designed with added thickness sufficient to offset anticipated corrosion loss. This of course increases the car weight substantially, again at the expense of operating economy. Such steel gondola railcars also require extensive painting and corrosion treatment, periodic repainting, resheeting, and the provision of interior linings which require periodic replacement, all of which further degrade their operating economy.
The use of aluminum instead of steel for the car material has been considered for some time as an economically attractive alternative for lowering fuel and other operating costs, together with maintenance-of-way costs. Aluminum provides a higher strength-to-weight ratio, along with the potential for reducing the weight of a corresponding steel car by approximately 20 percent. This of course can be translated into more payload capacity and hence a reduction in number of cars necessary to transport a given quantity of bulk material in a single train, fewer hauls and, in some cases, fewer locomotives. Additionally, since aluminum is corrosion resistant, it offers a longer service life and less maintenance, does not require painting or other protective coatings, can be fabricated using modern techniques, and does not require added material thickness to counteract corrosion effects. A further economic advantage is the higher scrap value of the aluminum.
Though the foregoing advantages of aluminum have been known for some time, most gondola railcars continue to be fabricated from steel. Those gondola railcars which are fabricated from aluminum, moreover, commonly are based upon steel car designs which, as discussed above, tend to be uneconomical. Thus, while some weight savings may be obtained by using aluminum, the basic gondola railcar design employed often imposes such inherent weight and cost penalties that the resultant aluminum car does not appear as an economical alternative to the corresponding steel gondola railcar.